The Mitsubishi HC7900DW projector definitely comes with a better than most warranty, for projectors near its price.
The Mitsubishi HC7900DW comes with a three year limited parts and labor warranty. In addition, it comes with a 10,000 hour warranty on the DLP chip. That last part is interesting, in that one never hears of a DLP chip failure. In the couple of years, though, several manufacturers using DLP chips have been providing the warranties on their chips. Hey, it can't hurt. Still, consider it mostly good marketing, rather than something needed.
In the price range, most projectors have two year warranties. There are even a few one year warranties. About the best are Optoma's HD8300, and Epson's Pro Cinema 6020 which have three year warranties. The Epson further provides a 48 hour replacement service for all three years, while Optoma's replacement service only covers the first year. This Mitsubishi HC7900DW projector's warranty is close behind. Those are all "authorized local dealer only" sold projectors.
In terms of the competing projectors sold online, the $2599 Epson HC5020 (basically the 6020 in white case) comes with 2 years with replacement warranty for both years. The Panasonic PT-AE8000 comes with two years, not three, but on top of that, they limit their warranty to 2000 hours of use maximum, an amount some heavy user owners will go through in less than one year.
JVC's DLA-RS46, and DLA-X35 offer two years, as does Acer with their less expensive H9500BD. BenQ provides only a single year warranty on their W7000.
The longest warranty of the competing projectors, ones which are sold over the internet, belongs to the Sony VPL-HW50ES. That's the only other one I can think of in the price range.
The bottom line: Three years is about as good as it gets. A replacement program would be nice, but the Mitsubishi HC7900DW warranty is as long as any other major brand, and longer than most.